The technology disclosed herein generally relates to Computed Tomography (CT) imaging systems. More specifically, the subject matter relates to systems and methods to recalibrate a monochromatic image received from a CT imaging system based on a petrous bone.
CT is a technology that uses X-rays to produce tomographic images (i.e., virtual slices) of a subject (e.g., a head/head-neck region of a human patient). The tomographic slices are then used to generate a three-dimensional (3D) CT image of the subject. Currently, multi-energy spectral CT systems have been developed that can determine densities of different materials in a subject and generate CT images acquired at multiple monochromatic X-ray energy levels. Typically, the multi-energy spectral CT systems include one or more X-ray sources for projecting one or more X-ray beams at a plurality of energy levels towards the subject. Although, an X-ray source projects one or more X-ray beams at a particular energy (e.g., 80 peak kilovoltages, 140 peak kilovoltages, and the like), the respective X-ray emissions at a given energy are actually along an energy continuum or spectrum and, therefore, constitute a polychromatic emission centered at, or having a peak strength at, the desired energy level. The multi-energy spectral CT systems further include one or more X-ray detection units that receive the one or more X-ray beams attenuated by the subject and generate polychromatic images of the subject. The X-ray detection units further generate monochromatic images of the subject that simulate how the subject would appear in an image, if the image were obtained based on a true monochromatic X-ray source, i.e., an X-ray source that projects an X-ray beam of a single energy level expressed in Kilo electron Voltage.
However, such multi-energy spectral CT scanners may generate erroneous monochromatic images due to multiple sources of variations, leading to incorrect measurements of image Hounsfield Units and density values. The multiple sources of variations include, for example, variations caused by the operation and the location of the X-ray sources, variations due to erroneous inputs from the administrators of the X-ray sources, variations in material densities across different subjects, and the like. Thus, there is a need for a system and method for recalibrating the monochromatic images.